1. Field of the Invention:
This invention relates to a device for stabilizing an image and, more particularly, to an image-stabilizing optical system arranged in front of a photographic system to optically compensate for the shake of a photographic image caused by the vibration (tilting) of the photographic system, so that a stationary image is obtained, thus achieving stabilization of the image when shooting. Still more particularly it relates to image-stabilizing optical systems suited to cameras for photography, video cameras, etc..
2. Description of the Related Art:
When shooting from a running car, flying aircraft, or other moving vehicle, vibrations propagate to the photographic system, causing the photographic image to shake.
To prevent the photographic image from shaking, a wide variety of image stabilization optical systems have been proposed.
For example, Japanese Patent Publication No. Sho 56-21133 shows an optical device responsive to the signal output from a sensor for detecting the vibrated state for moving an optical member constituting part of the photographic lens in such a direction as to cancel the accidental deflection of an image caused by the vibration when achieving stabilization of the image.
Japanese Laid-Open Patent Application No. Sho 61-223819 employs a variable-angle prism of the refractive type arranged at the frontmost position in constructing a photographic system so that the vertex angle of the refractive type variable-angle prism varies in correspondence to the displacement of the photographic system from the line of sight to thereby deflect the image, thus stabilizing the image.
Japanese Patent Publications Nos. Sho 56-34847 and Sho 57-7414 provide the photographic system with an optical member held in fixed spatial alignment with the line of sight against vibrations so that, as vibrations occur, a prism effect is produced by this optical member to deflect the line of sight rays through such an angle as to stabilize the image at the focal plane.
There is another method of stabilizing the image by moving part of the photographic system, or a lens group, in directions orthogonal to the optical axis through the proper distance derived from the output signal of an acceleration sensor for detecting vibrations of the photographic system.
Besides these U.S. Pat. No. 2,959,088 has proposed an afocal system comprising two lens groups of which the first is of negative power and the second is of positive power, their absolute values of the focal length being equal to each other. This system is arranged in front of a telescope and, as the telescope deviates from the line of sight, the second lens group is made to rotate around its focus at which the center of gyro gimbals as the supporter therefor is placed. According to this proposal, therefore, the image-stabilizing optical system utilizes the inertia pendulum method.
In general, the use of the front type of image stabilizer for the photographic system in combination with the free support of part of the optics of the stabilizer has a problem that the resultant stabilized optical system that compensates for the accidental shake of the photographic image increases largely in size. Another problem is that the amount of shake of the photographic image to be compensated for and the required amount of movement of the freely supported lens group fall in complicated relationship to each other. Therefore, the complexity of structure of the operating mechanism for the entirety of the image-stabilizing optical system comes to increase largely.
Still another problem is that the amount of aberrations produced by the movement of the freely supported lens group, or decentering aberrations, increases largely so the optical performance is largely lowered.
For example, in the aforesaid U.S. Pat. No. 2,959,088, the freely supported lens group by the gyro gimbals, or the second lens group, is made rotatable about a point on the optical axis away from its principal point by the focal length f.
To facilitate minimization of the range of variation of aberrations with rotation of the second lens group, it is preferred to make the focal length f of the second lens group as large as possible. The use of a large value of the focal length, however, brings its center of rotation to behind the photographic system, so that, for example, the position of the counter weight becomes very far from the second lens group, thus largely increasing the size of the image-stabilizing optical system.
To achieve a reduction of the size of the system, the focal length f of the second lens group may be made small. If so, a problem arises that the decentering aberrations by the second lens group increase objectionably.
As the related art, there are U.S. Patent Applications Ser. Nos. 346,512 filed on May 2, 1989 and 407,657 filed on Sept. 15, 1989.